The present invention relates to information recording media, and more particularly to a high molecular weight information recording medium which permits data bits to be written when the medium is heated to its glass (transition) temperature and polarized. The invention relates also to the method of writing data bits in such a high molecular weight information recording medium.
As a result of recent developments in electronic and telecommunications technology, the demand for high density recording (information storage) media has greatly increased. Currently, magnetic disks, CD-ROMs, and DVD-ROMs are most commonly used for storing data bits. Writing and reading data bits in these recording media are commonly achieved by means of the application of an electric field or be varying the optical characteristics of the medium. However, because of the limitations of mechanical precision and wavelength, it is difficult to improve the recording density of such recording media. In order to meet the demand for high density recording media, most recording media designers and manufacturers have invested a lot of money in developing ultra high density recording media suitable for repeatedly writing and reading data bits. The result has been the development of microscope scanning probe type storage technology, which involves using a microscopic scanning probe as the center of the writing mechanism for processing the material surface directly, so as to write information data in the recording medium by changing the number of the molecules, atoms, or electric charges. By means of this general method, the storage density can be greatly improved, for example, to several hundred times that of conventional CD-ROMs (several G bits/in.sup.2 to thousands of G bits/in.sup.2), which greatly reduces the unit cost of the medium.
There are several known methods of using a microscope scanning probe to write data bits in a recording medium. These methods include the thermo-mechanical data storage method, the charge storage method, and the gold dot storage method, summaries of which follow:
1. The Thermo-mechanical Data Storage Method
According to this method, a microscope scanning probe is adhered to a piezoelectric driving device, and the recording medium, which is usually in the form of a disk, is put on a low-speed precision air bearing. The speed of the air bearing relative to the microscope scanning probe is about 10-100 mm/s. A laser diode of 30 mW is focused onto the atomic force microscope scanning probe to increase its temperature to a level sufficient for softening the disk, and then the probe is driven by a piezoelectric ceramic at the end thereof to press out a mark on the disk.
The size of the mark is less than approximately several hundred angstoms, and the mark is composed of a pit surrounded by a ridge which is formed from the material displaced by the tip of the probe. This pattern represents a density of about 25 G bits/in.sup.2, a more than 20 times increase in area density compared with conventional optical recording. However, this method can only write data bits in the same disk for one time, and does not allow the storage data bits to be modified. Another drawback of this method is that the coarseness tolerances for the disk surface are extremely low. Furthermore, this method is subject to dust protection and vibration problems.
2. The Charge Storage Method
This method involves making a mark on the recording medium by concentrating the electric charges of a particular material on a particular area by means of an electric field. When reading, a small voltage is applied to between the probe and the recording medium. Because of the effect of the static electricity of electric charges in the recording material, the previous record is read out when scanning. Because the tip of the probe is tiny (on the order of several angstroms or several tens of nanometers), the data density is high. An example of this method is found in U.S. Pat. No. 5,216,661, entitled "ELECTRON DENSITY STORAGE DEVICE USING A STM". This method can achieve ultrahigh density data writing and reading requirements. However, the recording medium is not stable and is vulnerable to temperature variations, background radiation, light rays and humidity. As a result, data stored on this type of medium cannot be kept for long (about several weeks only). Furthermore, because the organometallic material for the recording medium is obtained through a special extracting or synthesizing technique, manufacture of the recording medium is not easy.
3. The Gold Dot Storage Method
According to this method, the microscope scanning probe is coated with a layer of gold, and a negative voltage is applied to the disk, which is made from silicon, causing gold atoms at the tip of the probe to be evaporated and adhered to the disk. Because the tip of the microscope scanning probe is tiny, and the number of atoms evaporated is small, a large number of tiny gold dots can be formed on the surface of the disk. Through a proper selection of the probe size, and proper settings of the voltage value, the actuating time and the contact force, minimized gold dots can be achieved. The storage density of this method can reach 100 G bits/in* or even 1 T bits/in*. However, this method wastes a lot of gold atoms, and therefore the service life of the probe is short. Furthermore, this method will change the surface profile of the recording material, preventing repeated storage.